Alkane isomerization on highly reduced Pd/Al2O3 catalysts. The crucial role of Pd-Al species

Highly reduced (at 500 and 600 degrees C) 1 wt% Pd/Al2O3 samples showed remarkable isomerization selectivity in n-hexane conversion, > 80%, in agreement with previous reports. The catalytic behavior of highly reduced Pd/Al2O3 becomes typical of platinum, the metal regarded as unique in alkane isomerization. Although not detected in low metal loaded catalysts, Pd-Al species evidenced by formation of Pd-Al alloys in 5 wt% metal loaded catalysts appear essential active sites responsible for n-hexane isomerization. Other possible reasons (contribution from alumina acidity and changes in the structure of metal surface) were analyzed and discarded. A mechanistic rationale for the improvement of n-hexane isomerization is outlined.